Synchronizing-signal separating apparatus



Jam-13, 1942. G. w. EDWARDS SYNGHRONIZiNG-SIGNAL :SEPARATING APPARATUS Fi led Nov. 17, 1959 2 Sheets-Sfieet 1 Picture Signals lmerruplion ll'l Field 'Pulse [Field Pulse Single lnlerruplion in Field Pulse FIG.2.

INVE TOR nm CD O .D. Q 4 4 5 6 m m H F F GEORGE W. E

DWARDS ATTORNEY Jan. 13, 1942. s. w. EDWARDS SYIICI'IFKHJIZINGr-SIG'NAL SEPARATING APPARATUS Filed Ndjr. 17, 1939 2 Sheets-Sheet 2 A W F IMAGE REPRODUGING DEVICE o o VIDEO- FREQUENCY AMPLIFIER pETEc ToR,

INTERMEDIATE- FREQUENCY AMPLIFIER OSCILLATOR MODULATOR RADIO- FREQUENCY AMPLIFIER 'INVENTOR GERGE W.

EDWARDS ATTDRNEY Patented Jan. 13, 1942 ,SYNCHRONIZING-SIGNAL SEPARATING APPARATUS George William Edwards, Wembley, England,

assignor to Hazeltine Corporation, a corporation of Delaware Application November 17, 1939, Serial No. 304,939

In Great Britain November 30, 1938 12 Claims.

This invention relates generally to apparatus for translating television signals, and more particularly to apparatus for separating line-synchronizing and field-synchronizing components from the video components of a composite television signal and from each other.

A characteristic feature of the television signal under discussion is that the picture or video components of the signal are represented by modulations of the carrier wave in one direction from a given datum and are accompanied by two sets of synchronizing pulses, one set, for example, the line-synchronizing pulses, represented by modulations of the carrier wave in the opposite direction from the datum, each of these departures lasting for a period T and being separated by intervals nT, where n is considerably greater than 1, and the other set, for example, field-synchronizing pulses, represented by modulations of the carrier wave from the datum in the said opposite direction, each of these departures lasting in all for a period mT, where m is considerably greater than 1, but being interrupted by restorations of the carrier wave to or towards the datum for a period not very different from T. The field-synchronizing pulses are separated by intervals long comparedv with mT.

In the British Broadcasting Company transmissions, for instance, the datum is 30 per cent. of the carrier amplitude, the first-named direction is an increase in carrier amplitude, the modulation in the opposite direction is a fall to zero, n=9, m=40; and the said interruptions consist of returns to the datum for a period T occurring at intervals (n+l)T/2. Hereinafter it will usually be assumed that the television signals to which reference is made in the specification are of the character just described and for brevity 'the change of the carrier amplitude in the first-named direction'is assumed to be a rise and that in the opposite direction, a fall, but nothing material would be changed if rise and fall were interchanged consistently throughout specification.

Again it will appear later that it is not necessary to the invention that there should be a plurality of interruptions during the field-synchronizing intervals mT, a single interruption being sufficient. The purpose for which the interruptions were originally introduced into the field-synchronizing pulse of period mT is not material to the present invention. However, the interruptions were not originally intended to acfield-synchronizing pulses; the field-scanning generator was originally intended to be actuated by the fall of the carrier amplitude at the start .of the intervals mT. Certain difficulties then arose from interference between the line-synchronizing pulses and field-synchronizing pulses. Various arrangements have been proposed in the prior art for mitigating these diificulties. In

. British Patent No. 484,412, for instance, one such principle underlying the arrangement of the British patent is to set the field-scanning generator into operation, not by the fall of the carrier amplitude at the start of the interval mT, but by the rise of the carrier amplitude when A it is first restored during this interval. In other the tuatethe field-scanning generator receiving the words, the field-scanning generator is actuated, not by the leading edge of the first field-synchronizing pulse, but by the interruption or trailing edge of the first field-synchronizing pulse.

In order to utilize this principle of operation, it is necessary to distinguish in some manner the rise in the carrier amplitude initiating an interruption in the field-synchronizing pulse and a rise in carrier amplitude terminating a line-synchronizing pulse, for the field-scanning oscillator must be actuated by the former and not by the latter. The arrangement for making this distinction particularly described in the British patent comprises, broadly, one for inserting in the path by which the pulses reach the field-scanning generator, but not in the path by which they reach the line-scanning generator, a circuit having a finite time constant considerably greater than T but not considerably greater than m'I.

Here it may be pointed out that the signals applied to the scanning generators are never in practice precisely those modulating the carrier wave emitted by the transmitter. The separation of the video-signal components from the synchronizing pulses is usually effected by a biased rectifier. The synchronizing pulses emerging'from the rectifier are, therefore, not variations in the strength of a carrier wave, but variations of a potential relative to some datum. A fall in carrier amplitude appears as a change of the potential in one direction and a rise as a change of the potential in the other direction. This transformation of the signals is assumed in the description'of the arrangement of the British patent and will be assumed hereinafter. However, if some other way of separating the videosignal components from the synchronizing pulses should be utilized, it might not prove to be essential to the arrangement of the present invention that the transformation should occur before the distinction between the line-synchronizing pulses and the interruptions in the fieldsynchronizing pulses is made.

An object of this invention, therefore, is to provide an improved arrangement for distinguishing interruptions or impulses in the fieldsynchronizing pulses from the line-synchronizing pulses or impulses thereof.

In accordance with the invention, a television synchronizing-signal separating system adapted to be energized by a composite synchronizing signal including line-synchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, the linesynchronizing pulses comprises means for deriving from the composite signal a signal having impulses corresponding in time with impulses of the field-synchronizing pulses of the composite signal. Means including a time-constant circuit eifective to suppress amplitude variations of duration appreciably less than th duration of the field-synchronizing pulses are provided for deriving a substantially continuous pulse initiating at the initiation of the field-synchronizing pulses and having a duration at least as great as any of the field-synchronizing pulses. Means are also provided for combining the derived signals with such relative polarities that the impulses occurring during the derived pulse are additive thereto and a field-scanning circuit is provided responsive only to amplitude values of the combined signal above a predetermined amplitude level. It is to be understood that the pulse initiating at the initiation of the fieldsynchronizing pulses need not have an appreciable finite amplitude at the beginning of the field-synchronizing pulses, it being suflicient that an integration is initiated at this time which may produce a maximum pulse amplitude at a later time.

In the specification and appended claims, the term pulse is employed in accordance with its conventional meaning to describe an amplitude variation in a signal which includes a departure from a given value and a subsequent return to such value after a greater or lesser period. The term impulse is employed to indicate a single amplitude variation in a signal. For instance, in a signal of rectangular wave form, each rectangular pulse comprises a leading edge constituting one impulse and a trailing edge constituting a second separate impulse. Either of these impulses may, of course, represent information to be utilized separately to effect a controlling action, if desired.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the accompanying drawings, Fig. 1. is a curve illustrating a type of television wave form which is utilized in some television systems and of the type to which reference is made in the second paragraph of this specification; Fig. 2 is a curve illustrating another type of composite synchronizing signal which may be utilized in the system of the present invention; Fig. 3 is a schematic diagram utilized to illustrate the general principles of the present invention; Figs. la-5a, inclusive, are graphs utilized to explain certain of the operating characteristics of the schematic diagram of Fig. 3; while Fig. 6 is a circuit diagram, partly schematic, of a portion of a television receiver of the superheterodyne type incorporating the invention as the synchronizing-signal separating apparatus thereof.

Referring now more particularly to Fig. 1 of the drawings, the curve represents the type of television signal normally utilized in certain conventional television systems. The composite synchronizing signal is represented by the fullline portion of the curve and comprises relatively narrow line-frequency pulses and relatively broad field-frequency pulses, each indicated by a suitable legend in the drawings. The picture information or video-frequency signal components of the transmitted signal correspond in time with the intervals between the line-synchronizing pulses and are indicated by the dotted-line portions designated as picture signals in the drawings.

Fig. 2 of the drawings illustrates another type of composite synchronizing signal which can be utilized with a synchronizing-signal separating arrangement in accordance with the present invention and difiers from that illustrated in Fig. 1 mainly in that only a single broad field-synchronizing pulse is utilized having a duration mT and containing a single interruption within this time interval. i

The characteristic feature of the invention is illustrated diagrammatically in Fig. 3 of the drawings. Here the synchronizing pulses separated from the picture signals arrive by the path I at the junction 0. Thence the path 2 leads to the line-scanning generator L and the path 3 to the field-scanning generator F. A generator G is provided the output of which travels along path 4 and is superimposed on the pulses passing along the path 3. In other words, parallel paths 3 and 5G-4 are provided for coupling the derived signals to the signal-translating stage F with such polarities that predetermined desired impulses occurring during a derived broad pulse, developed in generator G, are additive thereto in the signahtranslating stage F. The generator G is utilized to develop a pulse initiating at the initiation of the field-synchronizing pulses and having a duration at least as great as any of the field-synchronizing pulses. In the specific embodiment illustrated the developed pulse vanishes after a period independent of the duration of the field-synchronizing pulses. Preferably, as indicated by the dotted line 5, the generator G is controlled by the pulses arriving at 0; it may draw its energy from these pulses or may integrate the received field-synchronizing pulses, but this is not essential. Thus if power is supplied to a television receiving apparatus from the same alternating source which supplies the transmitting apparatus, it is possible for the generator G to operate directly by the power supply source.

One mode of utilizing the invention is illustrated, by way of example, by the curves of Figs. 4a and 4b of the drawings. Fig. 4a illustrates the pulse which may be derived by generator G, the pulse starting at the time X. in Fig. 1 and having the period mT, where mT is at least as great as any field-synchronizing pulse. That is, the pulse of Fig. 4a. initiates at the initiation of the field-synchronizing pulses, has a duration at least as great as any of the field-synchronizing a radio frequency amplifier.20 to which are con-.

pulses, and terminates beforethe series of fieldsynchronizing pulses following the series from which it was derived. Fig. 4b shows the result of superimposing the pulse of Fig. 411 on the synchronizing-signal wave form of Fig. 1. If the field-scanning generator is arranged so that it is set in operation when, and only when, an impulse reaches the critical level shown in Fig. 42), it will clearly respond to the first impulse of the interruption b of the field-synchronizing pulse but not to any line impulse.

It is to be observed that the accuracy with which the position of the critical level must be fixed, in order that the field-scanning generator F may be actuated by a particular interruption or impulse, is determined by the steepness of the disturbance, which: is, in principle, independent of the values of T and mT. In this respect .the invention differs from that described in the above-mentioned British Patent No. 484,412, for there the accuracy is limited by the condition that the time constant of the discriminating circuit shall be greater than T but not much greater than mT.

Another mode of utilizing the invention is illustrated by the curves of Figs. 5a and 5b of the drawings. It is known that, at times, it is desirable to pass the line-synchronizing pulses, separated from the picture signals, through a differentiating circuit, for example, a resistancecapacitance coupling, of time constant much less than T, so as to produce a pair of oppositely directed pulses, one corresponding to the front or leading edge and one to the back or trailing edge of an original line-synchronizing pulse. In the arrangement of the said British patent, this transformation cannot be applied to the interruptions of the field-synchronizing pulse by the discriminating circuit for the reason that the time constant of this circuit is necessarily greater than T. However, in the arrangement of the present invention, the coupling by which the impulses on which the pulse derived by generator G is superimposed are conveyed to the field-scanning generator can have any time constant, and

the said transformation can be produced by this coupling. By the use of a suitable differentiating coupling circuit of small time constant, the signals applied to the scanning generators can be given either the form of Fig. 5a or the form of Fig. 5b in a manner well understood by those skilled in the art. These curves show the signals to be applied to the field-scanning generator F comprising the differentiated pulses superimposed on the pulse of Fig. 4a, which is generated by the generator G, while the pulses applied to the line-scanning generator L are not superimposed on the pulse of Fig. 4a. These signals derived by differentiation are seen to comprise impulses corresponding in time with impulses of the field-synchronizing pulses of the composite signal. It is thus possible to apply positive control to one scanning generator and negative control to the other, as may sometimes be desirable It is thus seen that each of the curves of Figs. 4b, 5a, and 5?) have impulses corresponding in time with impulses of the line-synchronizing and field-synchronizing pulses of the composite synchronizing signal.

Fig. 6 of the drawings is a circuit diagram, partly schematic, of a complete television receiver of the superheterodyne type incorporating theinvention in the synchronizing-signal separating circuit thereof. The receiver comprises an antenna and ground system 2|, 22 connected to nected in cascade, in the order named, an oscillator-modulator 23, an intermediate-frequency amplifier 24, a detector 25, a video-frequency amplifier 26, and a cathode-ray signal-reproducing device 21. A line-frequency generator 28 and a field-frequency generator 29 are also coupledto the video-frequency amplifier 26 and connected to the scanning elements of the cathode-ray tube of signal-reproducing unit 21 in a conventional manner.

The stages or units 20-29, inclusive, may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are deemed unnecessary herein. Referring briefly, however, to the operation of the system described above, television signals intercepted by the, antenna circuit 2|, 22 are selected and am! plified in radio-frequency amplifier circuit 20 and supplied to the oscillator-modulator 23 wherein they are converted to intermediate-frequency signals which, in turn, are selectively amplified in the intermediate-frequency amplifier 24 and delivered to the detector 25. The modulation components of the signal are derived by the detector 25 and are supplied to the video-frequency amplifier 26 wherein they are amplified and from. which they are supplied in the usual manner to a brightness-control electrode of the signal-reproducing unit 21 and to the synchronizing control elements of the scanning generators 28 and 29 by means of the synchronizing-signal separator of the invention, to be described more fully hereinafter. The intensity of the scanningbeam of the device 21 is thus modulated or controlled in accordance with the video-frequency voltages impressed on the control electrode thereof in the usual manner. Saw-tooth current or voltage scanning waves are generated in the line-frequency and. field-frequency generators 28 and 29,. which are controlled by the synchronizing volt-,

age impulses supplied from the video-frequency amplifier 26, and applied to the scanning ele.-.-

ments of the device 21 to produce electric scanning fields, thereby to deflect the ray vertically and horizontally so as to trace a rectilinear scanning pattern on the screen of the device 21 and thereby reconstruct the transmitted picture.

Coming now to the portion of the system of Fig. 6 embodying the present invention, rectifier V1 is a biased rectifier whereby the synchronizing pulses of the received signal are separated from the composite video-signal components and synchronizing pulses applied to the input circuit of the tube. Impedance 8 is the main load of rectifier V1, so that the synchronizing pulses are developed between the junction 0 and ground. .The'

a tube L and to the field-scanning generator through a tube F. Each of the paths contains a capacitance-resistance coupling 0, R, having a time constant much less than T, so that the synchronizing signals received by the scanning generator F are of the character shown in Figs. 5a, and 5b, after superimposition on the pulse of Fig. 4a, rather than that shown in Fig. 4b. The values of C and R are not necessarily equal in the two paths.

The generator G of Fig. 3 is represented by a transformer G the primary winding 9 of which connects the point 0 to the anode of tube V1 and the secondary winding IU of which lies in the path 3. The inductive coupling between primary and secondary windings-of transformer G represents the path 4 of Fig. 3. Capacitance which may be only self-capacitance is associated with the windings of this transformer, as indicated by the dotted-line condenser C, so that the transformer has a time constant much greater than T and there is developed in its secondary winding a pulse having a period mT of the order of mT, initiating from the start of the field-synchronizing signals. This pulse is superimposed on the signals arriving by path 3.

By comparison of Figs. 5a and 512 it will be seen that the sign of the pulse generated by the transformer G must be suitably related to the sign of the impulse by which the field-scanning generator is to be actuated. If the field-scanning generator is to be actuated by the trailing edge of a field-synchronizing pulse, the derived pulse must be of one sign; if it is to be actuated by the leading edge of the succeeding field-synchronizing pulse, the derived pulse must be of the other sign. The sign can, of course, be chosen by proper poling of the windings 9 and [0.

It will be apparent that, if the capacitance between the windings of the transformer G is sufficient, it might be used as the capacitance C in the path 3; the condenser marked C might then be omitted entirely. In summary, therefore, it is seen that the television synchronizingsignal separating system of Fig. 6 is adapted to be energized by a composite synchronizing signal, including line-synchronizing pulses and fieldsynchronizing pulses of the same polarity as, but having a greater duration than, the line-synchronizing pulses, as represented by the composite synchronizing signal of Fig. 1 or Fig. 2. The system also comprises the transformer 9, ill for deriving from the composite Signal a signal having impulses corresponding in time with impulses of the field-synchronizing pulses of the composite signal, as illustrated by a, b, and c of any of the curves 4?), 5a., or 52), means comprising transformer 9, l0 and including a time-constant circuit effective to suppress amplitude variations of duration appreciably less than the duration '1 of the line-synchronizing pulses for developing a substantially continuous pulse initiating at the initiation of the field-synchronizing pulses and having a duration at least as great as any of the field-synchronizing pulses as illustrated by the curve of Fig. 4a, and means comprising the tube F. for combining the derived signals with such relative polarities that predetermined desired impulses occurring during the above-mentioned continuous pulse are additive thereto. The system also comprises a field-scanning circuit 29 responsive only to amplitude values of the combined signal above a predetermined amplitude level.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including linesynchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for deriving from said composite signal a signal having impulses corresponding in time with impulses of the fieldsynchronizing pulses of said composite signal, means including a time-constant circuit effective to suppress amplitude variations of duration appreciably less than the duration of said field-synchronizing pulses for developing a substantially continuous pulse initiating at the initiation of said field-synchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, means for combining said derived signals with such relative polarities that predetermined desired impulses occurring during said derived pulse are additive thereto, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

2. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including linesynchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for deriving from said composite signal a signal having impulses corresponding in time with impulses of the fieldsynchronizing pulses of said composite signal, means including a time-constant circuit efifective to suppress amplitude variations of duration appreciably less than the duration of said fieldsynchronizing pulses for deriving from said fieldsynclironizing pulses a substantially continuous pulse initiating at the initiation of said field-synchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, means for combining said derived signals with such relative polarities that predetermined desired impulses occurring during said derived pulse are additive thereto, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

3. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including line-synchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for deriving from said composite signal a signal having impulses corresponding in time with impulses of the line-synchronizing and field-synchronizing pulses of said composite signal, means including a time-constant circuit effective to suppress amplitude variations of duration appreciably less than the duration of said field-synchronizing pulses for deriving from said field-synchronizing pulses a substantially continuous pulse initiating at the initiation of said field-synchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, said last-mentioned derived pulse terminating before the series of field-synchronizing pulses following the series from which it was derived, means for combining said derived signals with such polarities that predetermined desired impulses occurring during said derived pulse are additive thereto, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

4. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including line-synchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for deriving from said composite signal a signal having impulses corresponding in time with impulses of the fieldsynchronizing pulses of said composite signal, means including a time-constant circuit eifective to suppress amplitude variations of duration appreciably less than the duration of said fieldsynchronizing pulses for deriving from said fieldsynchronizing pulses a substantially continuous pulse initiating at the initiation of said field-synchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, means for combining said derived signals with such polarities that predetermined desired impulses occurring during said derived pulse are additive thereto, means for limiting said signal to derive a signal comprising only said predetermined ones of said impulses, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

' 5. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including linesynchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means including a time-constant circuit effective to suppress amplitude variations of duration appreciably less than the duration of said field-synchronizing pulses for deriving from said field-synchronizing pulses a substantially continuous pulse initiating at the initiation of said field-synchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, means for adding said composite scanning synchronizing signal to said derived pulse with such polarity that predetermined desired impulses of said field-synchronizing pulses occurring during said derived pulse are additive thereto, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

6. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including line-synchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for differentiating said composite signal to derive a signal having impulses corresponding in time with impulses of the fieldsynchronizing pulses of said composite signal, means including a time-constant circuit efiective to suppress amplitude variations of duration appreciably less than the duration of said fieldsynchronizing pulses for deriving from said fieldsynchronizing pulses a substantially continuous pulse initiating at the initiation of said fieldsynchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, means for combining said differentiated signal with said derived pulse with such relative polarities that the predetermined desired impulses occurring during said derived pulse are additive thereto, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

'7. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including linesynchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for deriving from'said composite signal a signal having impulses corresponding in time with impulses of the fieldsynchronizing pulses of said composite signal, integrating means including a time-constant circuit efiective to suppress amplitude variations of duration appreciably less than the duration of said field-synchronizing pulses for deriving from said field-synchronizing pulses a substantially continuous pulse initiating at the initiation of said field-synchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, means for combining said derived signals with such relative polarities that predetermined desired impulses occurring during said derived pulses are additive thereto, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

8. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including linesynchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, a synchronizing-signal translating stage, means for deriving from said composite signal a signal having impulses corresponding in time with impulses of the field-synchronizing pulses of said composite signal, means including a time-constant circuit efiective to sup press amplitude variations of duration appreciably less than the duration of said field-synchronizing pulses for deriving from said field synchronizing pulses a substantially continuous pulse initiating at the initiation of said fieldsynchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, means comprising parallelpaths for coupling said derived signals to said signal-translating stage with such relative polarities that the predetermined desired impulses occurring during said derived pulse are additive thereto in said signal-translating stage, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

9. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including linesynchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, a synchronizing-signal translating stage, a transformer including primary and secondary windings, a condenser, means for applying said composite signal to said signaltranslating stage through said condenser and said secondary winding to derive a composite signal having impulses corresponding in time with impulses of the field-synchronizing pulses of said composite signal, means for applying said composite signal also to said primary winding, said transformer comprising appreciable capacitance associated therewith so that there is induced in said secondary winding in response to said primary excitation a substantially continuous pulse initiating at the initiation of said fieldsynchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, said transformer being poled so that derived signals are applied to said signal-translating stage with such relative polarities that predetermined desired impulses occurring during said derived pulse are additive thereto.

10. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including line-synchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for differentiating said composite signal to derive a signal having impulses corresponding in time with impulses of the field-synchronizing pulses of said composite signal, means including a time-constant circuit effective to suppress amplitude variations of duration appreciably less than the duration of said field-synchronizing pulses for deriving from said field-synchronizing pulses a substantially continuous pulse initiating at the initiation of said field-synchronizing pulses and having a duration at least as great as any of said fieldsynchronizing pulses, means for combining said derived signal with such relative polarities that the impulses corresponding in time with the trailing edge of the field-synchronizing pulses of said composite signal are additive thereto, and a fieldscanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

11. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including linesynchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for differentiating said composite signal to derive a signal having impulses corresponding in time with impulses of the field-synchronizing pulses of said composite signal, means including a time-constant circuit efiective to suppress amplitude variations of duration appreciably less than the duration of said field-synchronizing pulses for deriving from said field-synchronizing pulses a substantially continuous pulse initiating at the initiation of said field-synchronizing pulses and having a duration at least as great as any of said field-synchronizing pulses, means for combining said derived signal with such relative polarities that the impulses corresponding in time with the leading edge of the field-synchronizing pulses of said composite signal are additive thereto, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

12. A television synchronizing-signal separating system adapted to be energized by a composite scanning synchronizing signal including linesynchronizing pulses and field-synchronizing pulses of the same polarity as, but having a greater duration than, said line-synchronizing pulses comprising, means for deriving from said composite signal a signal having impulses corresponding in time with impulses of the fieldsynchronizing pulses of said composite signal, integrating means including a time-constant circuit efiective to suppress variations of duration appreciably less than the duration of said fieldsynchronizing pulses for deriving from said fieldsynchronizing pulses a substantially continuous pulse initiating at the initiation of said fieldsynchronizing pulses, having a duration at least as great as any of said field-synchronizing pulses, and vanishing after a period independent of the duration of the field-synchronizing pulses, means for combining said derived signals with such relative polarities that predetermined desired impulses occurring during said derived pulses are additive thereto, and a field-scanning circuit responsive only to amplitude values of the combined signal above a predetermined amplitude level.

GEORGE WILLIAM EDWARDS. 

